I found this picture in an image collection at The Chive called It’s nearly impossible to argue with kid logic. I believe 7-year-old Elijah had a perfectly good answer on number ten, yet the teacher marked it wrong. Isn't a fart a gas? Yet, it is. According to Wikipedia, farts are composed mostly of oxygen, nitrogen, carbon dioxide, hydrogen, and methane.
It's possible that the test required answers that were part of class discussion, but one gets the feeling that the teacher objected to the vulgarity of the term fart. If that was the case, she could have suggested the terms "flatulence" or "methane" as a substitute. Telling a child that a word is inappropriate is very different from telling a kid that he's wrong on a science test. After all, families who don't use the term "fart" are very likely to say "gas." Any 7-year-old knows they mean the same thing. What do you think?
(Image credit: Christine Lee)
You could consider "Hydrogen sulfide", which is actually gaseous under normal conditions.
Science is not amazing as such, but it has amazingly good self-healing powers.